A textile pressure sensor for the capacitive measuring of the pressure distribution on a surface is known for example from DE 37 04 870, and exhibits a matrix arrangement of strips of conductive foil which are isolated from each other. The arrangement is flexible but not extensible.
A generic pressure sensor 1 for the capacitive measuring of a pressure distribution on a surface which is known from WO 2005/121729 is shown in the appended FIG. 7. The pressure sensor 1 is mat-shaped, i.e. formed substantially flat, and comprises a first conductive structure 3 and a second conductive structure 5. Between the first and the second conductive structure, which comprise a woven fabric, there is arranged a dielectric intermediate element 7 which is designed to be reversibly compressible, for example made of felt or foam. The first and the second structure are therefore arranged lying opposite one another. The first structure 3, which in FIG. 7 forms the upper side of the textile pressure sensor 1, comprises a plurality of conductive regions 9, i.e. electrodes which are electrically isolated from each other. Each conductive region 9 is connected in each case via a connecting lead, not shown in FIG. 7, to an electric circuit for the purpose of supplying energy and for evaluation. That surface or side which comes into contact with an object, the pressure distribution of which is to be measured on the textile pressure sensor 1, in this case is designated the upper side of the textile pressure sensor 1. In the embodiment shown, the second structure 5 has a continuously conductive surface, but it is likewise conceivable to provide several conductive regions which are isolated from each other, corresponding to the first structure 3. The second structure 5 forms the underside of the textile pressure sensor 1, which is arranged substantially parallel to the upper side of the pressure sensor. Owing to the opposite arrangement of conductive regions, capacitors C are formed between the first structure 3 and the second structure 5 in regions of overlap 11.
A capacitive sensor which is constructed as an individual sensor is known from EP 1 927 825 A1. In this case, fabrics to which foils are applied as capacitor plates are used. The fabrics may also be in the form of knitted fabrics.
A similar construction in which conductive or non-conductive fabrics are used is known from US 2007/0248799 A1. Here too, the term “fabric” is also to be understood to mean knitted goods, i.e. knitted fabrics or warp-knitted fabrics. Here too, the known construction is very labor-intensive.
The method of operation of capacitive sensors is sufficiently known. They operate on the basis of the change in the capacitance of an individual capacitor or of a whole capacitor system. Virtually all capacitive sensors are based on the principle that two plates form an electrical capacitor, one plate of which is displaced or deformed by the effect which is to be measured. As a result, the plate spacing, and hence the electrically measurable capacitance, changes. In order also to be able to detect small changes better, the actual measuring electrode is frequently surrounded by a shielding electrode which shields the non-homogeneous edge region of the electric field from the measuring electrode. This yields an approximately parallel electric field with the known characteristic of an ideal plate-type capacitor between the measuring electrode and the usually earthed counter-electrode. In the case of a capacitive pressure sensor, the change in capacitance as a result of the deflection of a membrane and of the resulting change in the plate spacing is evaluated as a sensor effect. The membrane in this case is formed as a capacitor plate. The changes in capacitance are fairly small, so suitable processing electronics of high sensitivity must be integrated into it.
In relation to the textile pressure sensor 1, this means that for measuring a pressure distribution an object comes into contact with the upper side of the textile pressure sensor 1. The object in so doing exerts a compressive force on the textile pressure sensor 1 in the direction of the arrow 13, which brings about compression of the dielectric intermediate layer 7. In other words, the distance between the conductive regions 9 of the structures 3 and 5 is reduced where the force is exerted on the upper side of the textile pressure sensor 1 by the object.
The compression of the intermediate layer 7 and hence a reduction in the distance between the structures 3 and 5 is greatest where the greatest compressive force is exerted on the upper side of the textile pressure sensor 1. Correspondingly, the change in capacitance, which is detected by connected evaluation electronics, will be greatest in the regions of the greatest application of force or of the greatest pressure. The conductive regions 9 are preferably arranged in a matrix, and thus produce a matrix-shaped arrangement of capacitors C which preferably span the entire surface of the textile pressure sensor 1. Due to the detection of the capacitance and in particular of the change in capacitance of each capacitor C, a pressure-distribution pattern can thus be generated by the textile pressure sensor 1.
The use of textile pressure sensors of the type mentioned here is not restricted to a specific field. Rather, they can be used in many different ways, for example in the field of medical engineering, orthopaedics or sport. For example, textile pressure sensors can be used in medical engineering in order to avoid decubitus ulcers, i.e. local damage to the skin and the underlying tissue due to pressure being exerted on a patient's body parts. Such decubitus ulcers may for example occur in patients who are confined to bed or to a wheelchair. Textile pressure sensors can be used to measure the two-dimensional pressure distribution of a body part on an undersurface, for example on a mattress or the like, and to identify pressure points. In the field of medical engineering, furthermore the pressure distribution when a candidate is walking may for example provide information about orthopaedic damage or alternatively sensory damage (e.g. in diabetics).
In orthopaedics, textile pressure sensors of the type mentioned here may serve to detect the pressure distribution of a foot on the sole of a shoe. On the basis of the detected pressure distribution, the sole of the shoe can then be adapted, in particular by producing an individual insole, such that pressure peaks between the foot and the shoe material are avoided. In particular in the case of sports shoes or ski boots, such individual adaptation of shoes and boots is of particular interest. For example, it is of interest to the producer of sports shoes how the active forces are distributed across the foot surface of the wearer of the shoe during walking or running movements. Correspondingly, the shoes can be optimised according to the field of application. Resilient or supportive elements can accordingly be arranged in the shoe. This results in optimal adaptation of the shoe to the wearer, with the individual force distribution which occurs dependent on the anatomy of the wearer of the shoe and the sequences of movement thereof being taken into consideration. In the field of sport, a textile pressure sensor may furthermore serve to detect the pressure distribution in the production of skis, in order to be able to adapt a core structure accordingly. It is also conceivable in principle to use a textile pressure sensor for optimising bicycle saddles or equestrian saddles.
Further fields of application are pressure-sensitive floor coverings, in order to be able to detect a movement of an object or a load or a change in loading of a floor in a building in differentiated manner. Textile pressure sensors are further used in the field of synthetic skins for robots in order to reproduce tactile senses. Textile pressure sensors are also used for seating of any kind, in particular adaptive seats for aircraft, motor vehicles, drivers' cabs or in the private sphere, such as for example for office chairs. Textile pressure sensors are also used in the field of medical diagnostics for measuring the two-dimensional distribution of compressive forces. A further field of application is the measuring of muscle strength, in particular of sphincters at or in body orifices. Furthermore, it is conceivable to use textile pressure sensors in the field of video-game consoles, in particular for detecting a position and movements of a person and converting them into corresponding movements of gaming characters or gaming elements on a screen. Textile pressure sensors can also be used for identifying people, with the individual pressure-distribution patterns for example of a hand or a foot being used for unambiguous identification.
In summary, textile pressure sensors of the type mentioned here can be used everywhere where objects in general, and in particular body parts of a person, lie on a substantially solid substrate. Many objects and in particular body parts, the pressure distribution on a substrate of which is to be measured, are however not flat, but formed irregularly with elevations and depressions. Good adaptability to uneven objects and considerable robustness in the event of loading by such objects are thus a crucial quality criterion for textile pressure sensors. It has however been shown that the known textile pressure sensors for the capacitive measuring of a pressure distribution meet this quality criterion only to a limited extent.